This invention relates to a differential suited to be used for vehicles, etc.
The differential for vehicles includes a housing rotationally driven by an engine, a pair of side gears rotatably received in and coaxial with the housing and three pairs, for example, of element gears rotatably supported within the housing and meshed with the pair of side gears, respectively. The paired element gears are in mesh with each other. Thrust washers are disposed between end faces of the pair of side gears and between end faces of the pair of side gears and the housing. The pair of side gears are connected to end portions of a pair of coaxial output shafts, respectively.
In the differential thus constructed, if, for example, a vehicle wheel connected to one output shaft should go off a road, the output shaft would be idled (high-speed rotation) and no torque could be transmitted to the other vehicle wheel. As a consequence, there is the problem in that the off-road state cannot be removed.
In order to solve the above problem, in a differential which is disclosed in Japanese Laid-Open Patent Application Nos. Hei 2-66341 and Hei 2-142947, a pair of coned disk springs are interposed between a pair of side rears and a housing, respectively and the side gears are axially biased by the coned disk springs so that a so-called "preload" is acted on the side gears. Since a frictional resistance is generated between the side gears and the thrust washers by this preload, a torque can be transmitted to one output shaft even if the other output shaft is idled at a high speed.
Incidentally, since each side gear is spline-connected to a corresponding output shaft, when a torque is transmitted to the side gear through a meshing-engagement with the element gear, an axial vector of the torque is acted on the side gear as a thrust force. In the case where this thrust force acts outwardly, the side gear is moved toward the housing and pushes the coned disk spring through the thrust washer. When this coned disk spring is caused to take a flat plate-like configuration, the side gear is prohibited to move any further in the axial direction. Thereafter, when the thrust force is removed, the side gear is returned to its original position by the force of the coned disk spring. At that time, there is a possibility that the attitude of the coned disk spring is occasionally changed. For example, the attitude of the coned disk spring is changed from a state in which an outer peripheral edge of the coned disk spring is situated on the housing side with its inner peripheral edge being in contact with an end face of each side gear through the thrust washer to a state in which an inner peripheral edge, in turn, is situated on the housing side with its outer peripheral edge being in contact with the end face of each side gear through the thrust washer.
Before the attitude of the coned disk spring is changed, the inner peripheral portion of the thrust washer contacts the end face of the side gear harder than the outer peripheral portion does. Consequently, after the attitude of the coned disk spring is changed, the outer peripheral portion of the thrust washer contacts the end face of the side gear harder than the inner peripheral portion does. Therefore, the change of the attitude of the coned disk spring brings about a change of friction between the thrust washer and the side gear and eventually brings out a change of a distribution ratio of the torque.
As additional prior art to be listed here, there are EPC Patent No. 0130806 and U.S. Pat. No. 5,127,889. The EPC Patent No. 0130806 discloses a differential in which a coned disk spring is disposed between a pair of side gears. The U.S. Pat. No. 5,127,889 discloses a differential in which thrust washers are interposed between opposite ends of each element gear and a housing.